Diabetic Kidney Disease (DKD) is the leading microvascular cause of end-stage renal disease (ESRD) and cardiovascular disease (CVD), raising the mortality rate in type 2 diabetes mellitus (T2DM). DKD pathogenesis has traditionally been attributed to hemodynamic and metabolic factors induced by poor glycemic control and ageing-associated vascular changes [[1], [2], [3], [4]]. In recent research, immune cells, both locally in the kidney and systemically in circulation, are gaining traction for their pivotal role in the pathophysiology of DKD. Immune cell metabolism is said to undergo reprogramming due to a chronic hyperglycemic environment and increased glucose uptake into the cells. Increased glycolytic flux, overconsumption of oxygen by the gluconeogenic and oxidative pathways, metabolic hypoxia and ensuing mitochondrial oxidative stress are characteristics of the metabolic reprogramming observed in immune cells and proximal tubular epithelial cells in diabetic kidney disease models [[5], [6], [7], [8], [9]]. This phenomenon is entailed by the attainment of a pro-inflammatory phenotype by the immune cells through differentiation mechanisms such as macrophage polarization [[10], [11], [12]]. These pro-inflammatory immune cells infiltrate the renal interstitium, perpetuating tissue damage and fibrosis in the diabetic kidney [13,14].

NLRP3 inflammasome complex plays a vital role in the metabolic reprogramming, differentiation, and inflammatory behavior of the immune cells in T2DM [15,16]. Hyperglycemia induces metabolic changes such as increased glycolytic flux and HIFα induction, causing increased cellular oxidative free radical generation, AMPK inhibition, and decreased cytoplasmic NAD+ levels. These events result in NLRP3 activation and consequent release of IL-1β and IL-18 [[17], [18], [19], [20]]. Intra-renal activation of NLRP3 inflammasome expressed by infiltrating immune cells promotes inflammation, injury and fibrosis of renal tissue, culminating in renal functional decline [21]. Studies have also reported that NLRP3 inhibition prevented inflammatory cytokine release from immune cells and induced their shift from a pro-inflammatory phenotype to an anti-inflammatory phenotype, causing a reduction of fibrotic renal injury in animal DKD models and patients with kidney disease [22,23].

‘Inflamm-ageing’ describes the convergence of inflammatory pathways induced by ageing and metabolic sources (metaflammation) [13]. NLRP3 inflammasome activity is reported to be exacerbated in ageing individuals via impairing autophagy mechanisms, and the deletion of NLRP3 protected against the age-related increase in insulin resistance in aged mice [24,25]. Inflamm-ageing also involves impairment of the Heat Shock Protein (HSP) response. Mainly, decreased intracellular HSP72 is crucially involved in the dysregulation of metabolic checkpoints and impaired autophagy, thus enhancing insulin resistance and chronic inflammation, which are predominant in ageing and metabolic diseases. HSP72 is a chief chaperone protein protecting insulin signaling pathways and mitochondrial integrity against metabolic and oxidative stress. Impairment of HSP72 induction occurs in response to chronic hyperglycemia and ageing, causing exacerbated insulin resistance and oxidative stress-associated pro-inflammatory profile of cells [26]. DKD pathogenesis may involve inflamm-ageing mechanisms as the kidney ageing phenotype shares similarities with the diabetic kidney disease phenotype [27,28]. In these aspects, a shared and possibly inverse mechanistic association between the heat shock protein HSP72 and NLRP3 inflammasome seems likely in DKD. The role of NLRP3 is evident in diabetic renal tissue. However, kidney biopsy is not always possible for DKD patients. Therefore, understanding the expression of NLRP3 complex components in circulatory immune cells can elucidate its significance in systemic inflammation and progression of DKD non-invasively. This can lead to identifying non-invasive modalities to monitor disease progression based on the inflammatory signature of the circulatory immune cells. Furthermore, understanding the role of NLRP3 and its associated molecules in PBMCs may help determine the potential of NLRP3 inflammasome activation in circulatory immune cells as a possible measure of renal inflammatory damage status and DKD progression.

Backed by the above literature evidence, this study aimed to (i) assess the relative expression of NLRP3 inflammasome component genes in peripheral blood mononuclear leukocytes of type 2 diabetic patients with diabetic kidney disease and (ii) explore their relationship with the relative expression of intracellular HSP72 and kidney disease progression.